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Moon and Venus

July 10, 2013

The crescent Moon slides to the lower left of the planet Venus as night falls this evening. You can’t miss Venus because it’s the brilliant “evening star.”

Venus is so bright in part because it’s blanketed by clouds that reflect most of the sunlight that strikes them back into space. Because of these clouds, the surface of Venus actually receives less sunlight than Earth does, even though Earth is 26 million miles farther from the Sun. So logically, you might expect Venus to be cooler than Earth.

Yet Venus is actually the hottest planet in the solar system, with its surface roasting at 860 degrees Fahrenheit — hot enough to melt lead.

The reason for the discrepancy is simple: A planet’s temperature depends on more than just how much light it receives from the Sun — the planet’s atmosphere is also vital.

Earth is so far from the Sun that it ought to be an ice-covered world hostile to life. But our atmosphere contains small amounts of water vapor and carbon dioxide. After sunlight strikes and warms the surface, these gases prevent some of the warmth from escaping into space. That warms Earth by about 60 degrees, making it a perfect home for life.

But Venus takes this “greenhouse effect” to an extreme. Its atmosphere is much thicker than ours, and it consists almost entirely of carbon dioxide — a combination that makes Venus the hottest planet in the entire solar system.

We’ll talk about the Moon and another companion tomorrow.


Script by Ken Croswell, Copyright 2013

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